This application is a 371 of PCT/EP98/04678, filed Jul. 25, 1998.
1. Field of the Invention
The invention relates to agents and methods for permanent hair shaping containing as the keratin-reducing active ingredient an N,N-disubstituted mercaptoacetamide, to a method for producing such mercaptoacetamides and to the new mercaptoacetamide N-ethyl-N-2xe2x80x2-hydroxyethylmercaptoacetamide.
2. Prior Art
As is known, the conventional technique for achieving permanent hair shaping consists of two processing steps: In the first step, the cystine disulfide bonds of hair keratin are broken by the action of an agent containing a reducing substance (shaping agent). Then, the hair is shaped as desired. In a second step, the cystine disulfide bonds are reformed by means of a fixing agent, namely an agent containing an oxidizing substance.
As shown by the pioneering work described in German Patents 948 186 and 972 424, the conventional permanent wave reducing agent is thioglycolic acid used, for example, in the form of its ammonium or monoethanolamine salt. Other common reducing substances are inorganic sulfites, 2-mercaptopropionic acid (thiolactic acid), 3-mercaptopropionic acid, certain mercaptocarboxylic esters, cysteine and derivatives of these compounds.
All these agents, however, have a number of drawbacks. Alkaline preparations based on mercaptocarboxylic acids, in spite of adequate efficacy, cause hair damage manifesting itself, for example, by extensive hair breakage. Frequently, these agents also have an undesirable effect on the scalp. Finally, the unpleasant odor of the reducing agents used requires extensive addition of perfume to the products.
Some of said problems can be solved by use of 2-mercaptopropionic acid (thiolactic acid). Compared to the generally used thioglycolic acid, however, thiolactic acid has a weaker shaping effect.
The mercaptocarboxylic esters which permit hair shaping also at low pH values are unsatisfactory in terms of their skin tolerance and sensitization risk. In place of mercaptocarboxylic esters, mercapto acid amides such as thioglycolic acid amide or alkyl-substituted and hydroxyalkyl-substituted amides can be used. Such compounds are known from patents WO-A-91/10421 and EP-A-0 455 457. Like the carboxylic esters, these compounds have a high shaping potential also at low pH values, but in terms of their sensitizing properties are even worse than the esters.
The purpose of the invention is therefore to provide an agent and a method for permanent hair shaping which both in the acidic and in the alkaline range (pH=4.0 to 9.0) makes it possible to achieve uniform shaping and which has no sensitizing potential.
Surprisingly, we have now found that the said drawbacks can be avoided by use of N,N-disubstituted mercaptoacetamides having the following formula (I) and that these mercaptoacetamides have a higher shaping potential than thiolactic acid.
Hence, the object of the present invention is an agent for the permanent shaping of hair, characterized in that it contains as the keratin-reducing active ingredient a compound having the general formula 
or a salt thereof, wherein R1 and R2 denote a straight-chain or branched alkyl, monohydroxyalkyl or polyhydroxyalkyl or carboxyalkyl group, each with 1 to 6 carbon atoms.
Suitable salts of the mercaptoacetamides of formula (I) are all physiologically tolerated salts, particularly the hydrochloride, sulfate, phosphate, lactate, citrate and acetate.
Preferred are compounds in which R1 and R2 independently of each other denote CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, C(CH3)3, CH2CH(CH3)CH3, CH(OH)CH3, CH2OH, CH2CH2OH, CH2CH(OH)CH3, CH2CH2CH2OH, CH2CH(OH)CH2OH, CH(CH3)(CH2OH), CH(CH2OH)2 or CH2COOH.
Particularly preferred are compounds having the formulas 
The mercaptoacetamides of formula (I) are present in the ready-for-use hair shaping agent in an amount from 3 to 28 wt % and preferably from 5 to 21 wt %.
In another embodiment of the invention, the mercaptoacetamides of formula (I) can also be used in admixture with other, known thiols, such as thioglycolic acid, thiolactic acid, cysteine, cysteamine and alkyl- or acylcysteamines or sulfites.
The ready-for-use hair shaping agents preferably have a pH of 4.5 to 9.5 a pH, of 6.5 to 8.5 being particularly preferred. Suitable alkalizing and pH-adjusting agents are, in particular, ammonia or sodium hydroxide, but also water-soluble, physiologically tolerated salts of organic and inorganic bases, for example, ammonium hydrogen carbonate.
For marketing purposes, the shaping agents can be packaged as a one-component or a two-component system, the agent possibly being in the form of an aqueous solution or an emulsion or else in thickened, aqueous form, particularly as a cream, gel, foam or paste.
Naturally, the shaping agent can contain all known additives commonly used for such agents, for example, thickeners such as bentonite, fatty acids, starch, polyacrylic acid and derivatives thereof, cellulose derivatives, alginates, vaseline, paraffin oils; wetting agents or emulsifiers from the class of anionic, cationic, amphoteric or nonionic surface-active substances, for example fatty alcohols, fatty alcohol ether sulfates, alkylsulfonates, alkylbenzenesulfonates, quaternary ammonium salts, alkylbetaines, ethoxylated alkylphenols, fatty acid alkanolamides or ethoxylated fatty acid esters; moreover, opacifying agents, such as, for example, polyethylene glycol esters; alcohols, such as, for example, ethanol, propanol, polyols such as, for example, 1,2- or 1,3-propanediol, 1,2-, 1,3- or 1,4-butanediol, 1,2-, 1,3-, 1,4- or 1,5-pentanediol and glycerol; sugars such as, for example, D-glucose; solubilizers, stabilizers, buffers, scented oils, dyes and hair-conditioning and hair-care constituents, such as, for example cationic polymers, lanolin derivatives, cholesterol, pantothenic acid and betaine.
The additive ingredients are used in amounts commonly employed for such purposes. For example the wetting agents and emulsifiers are used at a total concentration of 0.2 to 30 wt %, the alcohols in a total amount of 0.1 to 20 wt %, the opacifying agents, scented oils and dyes in an amount of 0.01 to 1 wt % each, the buffers in a total amount of 0.1 to 10 wt %, sugar, solubilizers, stabilizers and hair-conditioning and hair-care agents in an amount of 0.1 to 5 wt % each, whereas the thickeners and solubilizers can be contained in said agent in a total amount of 0.5 to 20 wt %.
Moreover, for the purpose of enhancing the shaping agent""s efficacy, it is possible to add to it swelling agents and penetrants, for example dipropylene glycol monomethyl ether, 2-pyrrolidone or imidazolidin-2-one in an amount of 1 to 30 wt %, and for the purpose of preventing excessively tight hair curling dithio compounds, for example dithioglycolic acid, dithiolactic acid, the disulfides of said compounds or their salts.
By varying the pH, it is possible to provide an agent universally suitable for any hair structure, such an agent optionally being used in conjunction with heat. The agent brings about elastic, lasting and uniform shaping from the root to the tip of the hair without inducing allergic or sensitizing reactions.
Moreover, the present invention relates to a method for permanent hair shaping whereby the hair, before and/or after it was brought into the desired shape, is treated with a shaping agent, rinsed with water, treated with an oxidant, rinsed with water, optionally shaped to a wave using water only and then dried, said method being characterized in that the afore-described agent of the invention is used as the shaping agent.
According to a preferred embodiment of the method of the invention, the hair is first washed with a shampoo and then rinsed with water. The towel-dried hair is then divided into individual strands and wrapped onto a curler with a diameter of 5 to 30 millimeters and preferably 5 to 15 millimeters. The hair is then treated with an amount of the described shaping agent of the invention sufficient for hair shaping, preferably with 60 to 120 grams.
After a period of time sufficient for permanent shaping of the hair which, depending on the hair structure, pH, shaping efficacy of the shaping agent and use temperature, lasts from 5 to 30 min (10 to 30 min if no heat is used; 5 to 20 min with heating), the hair is rinsed with water and then post-treated (xe2x80x9cfixedxe2x80x9d) with an oxidant. The post-treatment agent is preferably used in an amount of 80 to 100 grams, depending on hair fullness.
For the oxidizing post-treatment in the wrapped or unwrapped state, any post-treatment agent suitable for such treatment can be used. Examples of oxidants that can be used in such post-treatment agents are potassium and sodium bromate, sodium perborate, urea peroxide and hydrogen peroxide. The concentration of the oxidant varies depending on the application time (as a rule 5 to 15 min) and the application temperature. The oxidant is usually present in the ready-for-use aqueous post-treatment agent at a concentration of 0.5 to 10 wt %. The agent for the oxidizing post-treatment can, of course, also contain other substances, for example wetting agents, care materials such as cationic polymers, weak acids, buffers or peroxide stabilizers, and it can be in the form of an aqueous solution, an emulsion or in thickened form on an aqueous basis, particularly as a cream, gel or paste. In particular, these common additives can be contained in the post-treatment agent in an amount of 0.1 to 10 wt %.
The curlers are then removed. If necessary, the unwrapped hair is subjected to another oxidizing treatment. The hair is then rinsed with water, optionally set to a wave using water only and then dried.
Another object of the invention is a method for making the mercaptoacetamides of formula (I) whereby an appropriate secondary amine is made to react with methyl thioglycolate at a temperature not exceeding 30xc2x0 C. Said method is described more closely in Preparation Example 1, method A, and Preparation Examples 2, 4 and 5.
Yet another object of the invention is the novel N-ethyl-N-2xe2x80x2-hydroxyethylmercaptoacetamide, obtained by the afore-described method.